Most of our daily activities are performed at light levels where vision is based on cone photoreceptors. A feature of cone-based vision is the capacity to see in color. Color is an important component of the information that we gather with our eyes; we use color so automatically that we fail to appreciate how important it is. It serves as a non-linguistic code that gives us instant information about the world around us. Common inherited variations in color vision provide a unique system in which to study the effects of alterations in the cone mosaic on visual function and how a variation in the amino acid sequence of the cone opsin affects cone photoreceptor function. The long-term goals of the proposed research are to understand the molecular genetics of cone-based vision, and to understand the relationship between genotype and phenotype. A practical application of this work is the development of a genetic test to distinguish between inherited color vision deficiencies, and color vision loss acquired secondary to disease or exposure to toxic chemicals or drugs. The specific aims are: 1) To determine the distribution of variation in the L:M cone ratio in the color normal population and to determine the extent to which the L:M cone ratio is specified by the X-chromosome visual pigment gene locus. 2) To investigate the effects of naturally occurring differences in primary amino acid sequence of X-encoded cone pigments on function, specifically with regard to alterations in cone spectral sensitivity and optical density. 3) To investigate specific phenotype/genotype relationships underlying color vision deficiencies with regard to a) the role of deleterious mutations in cone pigments in vision disorders; b) the molecular basis for variation in the severity of protan color vision defects; and c) the molecular genetic basis for color vision loss in males with a very mild defect but with normal looking pigment gene arrays, and females carriers who exhibit color vision abnormalities. To achieve these goals we will take a multidisciplinary approach, using psychophysical, electrophysiological and molecular biological techniques.